EP3623408A1 - Poly(lactic acid)-grafted cellulose nanofiber and production method therefor - Google Patents
Poly(lactic acid)-grafted cellulose nanofiber and production method therefor Download PDFInfo
- Publication number
- EP3623408A1 EP3623408A1 EP18798416.6A EP18798416A EP3623408A1 EP 3623408 A1 EP3623408 A1 EP 3623408A1 EP 18798416 A EP18798416 A EP 18798416A EP 3623408 A1 EP3623408 A1 EP 3623408A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- polylactide
- grafted
- cellulose nanofiber
- cellulose
- cnf
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 229920002678 cellulose Polymers 0.000 title claims abstract description 145
- 239000001913 cellulose Substances 0.000 title claims abstract description 145
- 239000002121 nanofiber Substances 0.000 title claims abstract description 100
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 30
- -1 Poly(lactic acid) Polymers 0.000 title description 4
- 229920000747 poly(lactic acid) Polymers 0.000 claims abstract description 79
- 238000002835 absorbance Methods 0.000 claims abstract description 51
- 238000010559 graft polymerization reaction Methods 0.000 claims abstract description 28
- VHYFNPMBLIVWCW-UHFFFAOYSA-N 4-Dimethylaminopyridine Chemical compound CN(C)C1=CC=NC=C1 VHYFNPMBLIVWCW-UHFFFAOYSA-N 0.000 claims abstract description 18
- 239000002685 polymerization catalyst Substances 0.000 claims abstract description 17
- 150000001412 amines Chemical class 0.000 claims abstract description 15
- 239000002253 acid Substances 0.000 claims abstract description 11
- RGGFMFZQWTZKDV-UHFFFAOYSA-N n,n-dimethylpyridin-1-ium-4-amine;trifluoromethanesulfonate Chemical compound [O-]S(=O)(=O)C(F)(F)F.CN(C)C1=CC=[NH+]C=C1 RGGFMFZQWTZKDV-UHFFFAOYSA-N 0.000 claims abstract description 11
- JJTUDXZGHPGLLC-UHFFFAOYSA-N lactide Chemical compound CC1OC(=O)C(C)OC1=O JJTUDXZGHPGLLC-UHFFFAOYSA-N 0.000 claims abstract description 9
- 150000003839 salts Chemical class 0.000 claims abstract description 7
- 238000000862 absorption spectrum Methods 0.000 claims abstract description 6
- 239000012778 molding material Substances 0.000 abstract description 11
- 239000002134 carbon nanofiber Substances 0.000 description 62
- 239000000835 fiber Substances 0.000 description 27
- 238000002425 crystallisation Methods 0.000 description 22
- 230000008025 crystallization Effects 0.000 description 22
- 238000002329 infrared spectrum Methods 0.000 description 19
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 16
- 238000000034 method Methods 0.000 description 16
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 14
- 238000002844 melting Methods 0.000 description 13
- 230000008018 melting Effects 0.000 description 13
- YMWUJEATGCHHMB-UHFFFAOYSA-N Dichloromethane Chemical compound ClCCl YMWUJEATGCHHMB-UHFFFAOYSA-N 0.000 description 12
- 238000011282 treatment Methods 0.000 description 12
- 238000009826 distribution Methods 0.000 description 11
- 239000000126 substance Substances 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 10
- 238000005259 measurement Methods 0.000 description 10
- 239000002245 particle Substances 0.000 description 10
- 238000006116 polymerization reaction Methods 0.000 description 10
- 239000007787 solid Substances 0.000 description 10
- 239000006185 dispersion Substances 0.000 description 9
- JJTUDXZGHPGLLC-IMJSIDKUSA-N 4511-42-6 Chemical compound C[C@@H]1OC(=O)[C@H](C)OC1=O JJTUDXZGHPGLLC-IMJSIDKUSA-N 0.000 description 8
- 238000000113 differential scanning calorimetry Methods 0.000 description 8
- 230000000694 effects Effects 0.000 description 8
- 239000007788 liquid Substances 0.000 description 8
- 239000000047 product Substances 0.000 description 8
- 239000011347 resin Substances 0.000 description 8
- 229920005989 resin Polymers 0.000 description 8
- 239000002904 solvent Substances 0.000 description 8
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 8
- 229920001131 Pulp (paper) Polymers 0.000 description 7
- 230000009477 glass transition Effects 0.000 description 7
- 239000000843 powder Substances 0.000 description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 229920002988 biodegradable polymer Polymers 0.000 description 6
- 239000004621 biodegradable polymer Substances 0.000 description 6
- 239000002655 kraft paper Substances 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 229920000642 polymer Polymers 0.000 description 5
- 239000006228 supernatant Substances 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 4
- 238000006243 chemical reaction Methods 0.000 description 4
- 239000003795 chemical substances by application Substances 0.000 description 4
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- 239000012766 organic filler Substances 0.000 description 4
- 238000000746 purification Methods 0.000 description 4
- JOXIMZWYDAKGHI-UHFFFAOYSA-N toluene-4-sulfonic acid Chemical compound CC1=CC=C(S(O)(=O)=O)C=C1 JOXIMZWYDAKGHI-UHFFFAOYSA-N 0.000 description 4
- ITMCEJHCFYSIIV-UHFFFAOYSA-N triflic acid Chemical compound OS(=O)(=O)C(F)(F)F ITMCEJHCFYSIIV-UHFFFAOYSA-N 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- RWRDLPDLKQPQOW-UHFFFAOYSA-N Pyrrolidine Chemical compound C1CCNC1 RWRDLPDLKQPQOW-UHFFFAOYSA-N 0.000 description 3
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 description 3
- 125000003178 carboxy group Chemical group [H]OC(*)=O 0.000 description 3
- 238000001125 extrusion Methods 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- 239000011121 hardwood Substances 0.000 description 3
- RAXXELZNTBOGNW-UHFFFAOYSA-N imidazole Natural products C1=CNC=N1 RAXXELZNTBOGNW-UHFFFAOYSA-N 0.000 description 3
- 239000000155 melt Substances 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 238000000465 moulding Methods 0.000 description 3
- 239000012299 nitrogen atmosphere Substances 0.000 description 3
- 125000002270 phosphoric acid ester group Chemical group 0.000 description 3
- 239000002002 slurry Substances 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- PAYRUJLWNCNPSJ-UHFFFAOYSA-N Aniline Chemical compound NC1=CC=CC=C1 PAYRUJLWNCNPSJ-UHFFFAOYSA-N 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 2
- 229920003043 Cellulose fiber Polymers 0.000 description 2
- BAVYZALUXZFZLV-UHFFFAOYSA-N Methylamine Chemical compound NC BAVYZALUXZFZLV-UHFFFAOYSA-N 0.000 description 2
- JUJWROOIHBZHMG-UHFFFAOYSA-N Pyridine Chemical compound C1=CC=NC=C1 JUJWROOIHBZHMG-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 229920001400 block copolymer Polymers 0.000 description 2
- 125000002915 carbonyl group Chemical group [*:2]C([*:1])=O 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 238000010101 extrusion blow moulding Methods 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 239000000945 filler Substances 0.000 description 2
- 238000001914 filtration Methods 0.000 description 2
- 238000004108 freeze drying Methods 0.000 description 2
- 125000000524 functional group Chemical group 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000010550 living polymerization reaction Methods 0.000 description 2
- 238000009996 mechanical pre-treatment Methods 0.000 description 2
- 244000005700 microbiome Species 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 229920005604 random copolymer Polymers 0.000 description 2
- 239000002994 raw material Substances 0.000 description 2
- DEXFNLNNUZKHNO-UHFFFAOYSA-N 6-[3-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-3-oxopropyl]-3H-1,3-benzoxazol-2-one Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)C(CCC1=CC2=C(NC(O2)=O)C=C1)=O DEXFNLNNUZKHNO-UHFFFAOYSA-N 0.000 description 1
- 102000004190 Enzymes Human genes 0.000 description 1
- 108090000790 Enzymes Proteins 0.000 description 1
- PIICEJLVQHRZGT-UHFFFAOYSA-N Ethylenediamine Chemical compound NCCN PIICEJLVQHRZGT-UHFFFAOYSA-N 0.000 description 1
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 1
- 239000004902 Softening Agent Substances 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 229920006362 Teflon® Polymers 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 239000012773 agricultural material Substances 0.000 description 1
- 150000003973 alkyl amines Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 1
- 150000001413 amino acids Chemical class 0.000 description 1
- 150000004982 aromatic amines Chemical class 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000007385 chemical modification Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- RTZKZFJDLAIYFH-UHFFFAOYSA-N ether Substances CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 1
- 238000000855 fermentation Methods 0.000 description 1
- 230000004151 fermentation Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 230000007062 hydrolysis Effects 0.000 description 1
- 238000006460 hydrolysis reaction Methods 0.000 description 1
- 230000005660 hydrophilic surface Effects 0.000 description 1
- 230000002209 hydrophobic effect Effects 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
- 239000003999 initiator Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000001746 injection moulding Methods 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 238000007561 laser diffraction method Methods 0.000 description 1
- 239000003550 marker Substances 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- GDOPTJXRTPNYNR-UHFFFAOYSA-N methyl-cyclopentane Natural products CC1CCCC1 GDOPTJXRTPNYNR-UHFFFAOYSA-N 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- OAOSXODRWGDDCV-UHFFFAOYSA-N n,n-dimethylpyridin-4-amine;4-methylbenzenesulfonic acid Chemical compound CN(C)C1=CC=NC=C1.CC1=CC=C(S(O)(=O)=O)C=C1 OAOSXODRWGDDCV-UHFFFAOYSA-N 0.000 description 1
- NNRDTRXBVBOCAG-UHFFFAOYSA-N n,n-dimethylpyridin-4-amine;hydrochloride Chemical compound Cl.CN(C)C1=CC=NC=C1 NNRDTRXBVBOCAG-UHFFFAOYSA-N 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000002667 nucleating agent Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 229910052762 osmium Inorganic materials 0.000 description 1
- SYQBFIAQOQZEGI-UHFFFAOYSA-N osmium atom Chemical compound [Os] SYQBFIAQOQZEGI-UHFFFAOYSA-N 0.000 description 1
- 239000000123 paper Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- UMJSCPRVCHMLSP-UHFFFAOYSA-N pyridine Natural products COC1=CC=CN=C1 UMJSCPRVCHMLSP-UHFFFAOYSA-N 0.000 description 1
- 239000011541 reaction mixture Substances 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
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- 238000003786 synthesis reaction Methods 0.000 description 1
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- 238000012546 transfer Methods 0.000 description 1
- 238000011179 visual inspection Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B15/00—Preparation of other cellulose derivatives or modified cellulose, e.g. complexes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
- C08B3/00—Preparation of cellulose esters of organic acids
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/06—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from hydroxycarboxylic acids
- C08G63/08—Lactones or lactides
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G81/00—Macromolecular compounds obtained by interreacting polymers in the absence of monomers, e.g. block polymers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/16—Nitrogen-containing compounds
- C08K5/34—Heterocyclic compounds having nitrogen in the ring
- C08K5/3412—Heterocyclic compounds having nitrogen in the ring having one nitrogen atom in the ring
- C08K5/3432—Six-membered rings
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
- C08L1/08—Cellulose derivatives
- C08L1/10—Esters of organic acids, i.e. acylates
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L101/00—Compositions of unspecified macromolecular compounds
- C08L101/16—Compositions of unspecified macromolecular compounds the macromolecular compounds being biodegradable
Definitions
- the present invention relates to a polylactide-grafted cellulose nanofiber and a production method thereof.
- biodegradable polymers that can be decomposed in natural environment due to actions of microorganisms existing in soil and water have attracted attention, and a variety of biodegradable polymers are developed.
- Atypical example of the biodegradable polymer is a polylactide.
- the polylactide is characterized by comparatively low cost, and is expected as a biodegradable polymer that is melt moldable.
- the polylactide has superior characteristics among the biodegradable polymers, due to having properties of being rigid and comparatively fragile as well as poorly flexible, compared with multipurpose polymers, it is necessary to add a softening agent in cases of manufacturing a molded product using the polylactide as a raw material.
- the polylactide has still insufficient heat resistance, and somewhat lacks in microwave-oven resistance.
- the polylactide also has properties of insufficient melting characteristics required in extrusion molding as well as blow molding and expansion molding.
- Patent Document 1 Japanese Unexamined Patent Application, Publication No. 2005-35134
- the present invention was made in view of the foregoing circumstances, and an object of the invention is to provide a polylactide-grafted cellulose nanofiber that is suitable as a molding material, and a production method thereof.
- cellulose nanofiber as referred to herein means a fine cellulose fiber that can be obtained by defibration of a biomass such as pulp fibers, and in general, means a cellulose fiber that includes cellulose fine fibers having a width of nano size (no less than 1 nm and no greater than 1,000 nm).
- a production method of a polylactide-grafted cellulose nanofiber includes carrying out graft polymerization of a lactide to cellulose constituting a cellulose nanofiber in the presence of an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid.
- an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid is used as a catalyst for the graft polymerization.
- a graft polymerization reaction of the polylactide to the cellulose proceeds in a living polymerization manner, thereby enabling the polylactide-grafted cellulose nanofiber to be obtained accompanied by molecular weight distribution of the polylactide with a sharp pattern.
- organic polymerization catalyst 4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate are preferred.
- the graft polymerization reaction of the polylactide to the cellulose described above can be more promoted.
- the graft polymerization is preferably repeated multiple times.
- the production method of a polylactide-grafted cellulose nanofiber enables the graft polymerization reaction of the polylactide to the cellulose nanofiber to proceed efficiently, and therefore mass productivity of the polylactide-grafted cellulose nanofiber is more improved.
- the polylactide-grafted cellulose nanofiber and the production method of the aspects of the present invention enable a polylactide-grafted cellulose nanofiber that is suitable as a molding material and a surface-modified organic additive material to be obtained.
- the cellulose nanofiber (hereinafter, may be also referred to as "CNF") is a fiber that includes fine fibers obtained by subjecting a biomass such as pulp fibers that include cellulose to a chemical or mechanical treatment.
- CNF cellulose nanofiber
- As a production method of the cellulose nanofiber there exist options in which cellulose per se is modified, and in which cellulose is not modified. In exemplary methods in which cellulose per se is modified, a part of hydroxyl groups of cellulose is modified to a carboxy group, a phosphoric acid ester group, etc. Of these, the method in which cellulose per se is not modified is preferred, and the reason therefor may be inferred as in the following, for example.
- a hydroxyl group serves as a starting point, whereas a carboxy group serves as a termination point. Since a cellulose nanofiber is used as an initiator for the polylactide-grafted cellulose nanofiber, a hydroxyl group of the cellulose nanofiber serves as the starting point of the reaction. Therefore, in the case in which a part of the hydroxyl groups of the cellulose is modified to a carboxy group, a phosphoric acid ester group, etc., the starting points of the graft polymerization reaction of the polylactide decrease, and thus the cellulose nanofiber not having been chemically modified is preferably used.
- the cellulose nanofiber not having been chemically modified is exemplified by a cellulose nanofiber microfabricated by a mechanical treatment.
- the modification amount of the hydroxyl groups of the cellulose nanofiber obtained is preferably no greater than 0.5 mmol/g, more preferably no greater than 0.3 mmol/g, and still more preferably no greater than 0.1 mmol/g.
- pulp fiber examples include:
- bleached chemical pulp (LBKP, NBKP) which contains as a principal component, cellulose having a large number of hydroxyl groups that serve as starting points of the reaction of polymerization for the polylactide.
- a chemical or mechanical pretreatment may be carried out in an aqueous system.
- the pretreatment is carried out for reducing the energy for mechanical defibration in the microfabrication step which will follow.
- the pretreatment is not particularly limited as long as a procedure for the pretreatment is employed in which modification of a functional group of cellulose of the cellulose nanofiber is not caused, and the reaction in an aqueous system enabled.
- the cellulose nanofiber is preferably produced by a method in which the functional group of cellulose is not modified.
- a primary hydroxyl group of cellulose is preferentially oxidized by using a treatment agent in the chemical pretreatment of the pulp fiber in the slurry, with an N-oxyl compound such as a 2,2,6,6-tetramethyl-1-piperidine-N-oxy (TEMPO) radical as a catalyst, as well as a method in which a phosphoric acid-based chemical is used to modify the hydroxyl group with a phosphoric acid ester group.
- TEMPO 2,2,6,6-tetramethyl-1-piperidine-N-oxy
- the cellulose nanofibers exhibit a single peak on a pseudo particle size distribution curve obtained by a measurement with a laser diffraction method in a state of having been dispersed in water.
- the particle diameter corresponding to the peak on the pseudo particle size distribution curve (i.e., most frequently found diameter) is preferably no less than 5 ⁇ m and no greater than 60 ⁇ m. In the case in which the cellulose nanofibers exhibit such particle size distribution, favorable performances owing to sufficient microfabrication can be achieved.
- particle size distribution curve means a curve indicating particle size distribution based on the volume as measured by using a particle size distribution measuring equipment (for example particle size distribution analyzer of laser diffraction scattering type, available from Seishin Enterprise Co., Ltd.).
- the average fiber diameter of the cellulose nanofibers is no less than 4 nm and no greater than 1,000 nm. It is considered that through miniaturization of the fibers to the average fiber width described above, the number of fibers in a molten resin per weight is increased, thereby enabling contribution to an increase in melt viscosity of the resin.
- the average fiber diameter is measured by the following method.
- One hundred milliliter of a dispersion liquid of the cellulose nanofibers in water having a solid content concentration of no less than 0.01% by mass and no greater than 0.1% by mass is filtered through a membrane filter made of Teflon (registered trademark), and solvent replacement is conducted with t-butanol.
- freeze drying is carried out and coating with a metal such as osmium gives a sample for observation.
- an observation is performed by electron microscopic SEM imaging at any magnification of 3,000 times, 5,000 times, 10,000 times or 30,000 times, in accordance with widths of constituting fibers. Specifically, two diagonal lines are drawn on an image for observation, and three straight lines that pass the intersection of the diagonal lines are arbitrarily drawn. Furthermore, widths of 100 fibers in total that cross these three straight lines are measured by visual inspection. Then, a middle diameter of the measurements is determined as the average fiber diameter.
- the lower limit of the degree of crystallization of the cellulose nanofibers is preferably 10%, more preferably 15%, and still more preferably 20%.
- the degree of crystallization is less than 10%, the strength of the fibers per se is deteriorated, and therefore an effect of improving the melt viscosity may be impaired.
- the upper limit of the degree of crystallization of the cellulose nanofibers is not particularly limited, but is preferably no greater than 95%, and more preferably no greater than 90%.
- degree of crystallization is arbitrarily adjustable by way of, for example, selection of pulp fibers, the pretreatment, the miniaturization treatment, etc.
- the degree of crystallization is a value measured by a X-ray diffraction analysis in accordance with "general rules for X-ray diffraction analysis” of JIS-K0131 (1996). It is to be noted that cellulose nanofiber has amorphous parts and crystalline parts, and the degree of crystallization means the proportion of crystalline parts in the entirety of the cellulose nanofibers.
- the lower limit of the pulp viscosity of the cellulose nanofiber is preferably 0.1 cps, and more preferably 0.5 cps.
- the pulp viscosity is less than 0.1 cps, resulting from a low degree of polymerization of the cellulose nanofibers, a fibrous state may not be maintained during the polymerization reaction for the polylactide, and the effect of improving the melt viscosity may be impaired.
- the upper limit of the pulp viscosity of the cellulose nanofiber is preferably 50 cps, and more preferably 40 cps.
- the pulp viscosity is greater than 50 cps, the degree of polymerization of the cellulose nanofiber per se is so great that the fiber is too long, whereby sufficient inhibition of aggregation of cellulose nanofibers may fail in the polymerization reaction for the polylactide, and thus the polymerization reaction for the polylactide may proceed nonuniformly.
- the pulp viscosity is measured in accordance with JIS-P8215 (1998). It is to be noted that a greater pulp viscosity indicates a greater degree of polymerization of the cellulose.
- the lower limit of type B viscosity of the dispersion liquid is preferably 1 cps, more preferably 3 cps, and still more preferably 5 cps.
- the type B viscosity of the dispersion liquid is less than 1 cps, the fibrous state may not be maintained during the polymerization reaction for the polylactide, and the effect of improving the melt viscosity may be impaired.
- the upper limit of the type B viscosity of the dispersion liquid is preferably 7,000 cps, more preferably 6,000 cps, and still more preferably 5,000 cps.
- the type B viscosity is measured on a dispersion liquid of the cellulose nanofibers in water having a solid content concentration of 1%, in accordance with "methods for viscosity measurement of liquid" of JIS-Z8803 (2011).
- the type B viscosity is a resistance torque in stirring a slurry, and a greater type B viscosity indicates a greater energy being required for the stirring.
- the upper limit of the water-holding capacity of the cellulose nanofiber is preferably 600%, more preferably 580%, and still more preferably 560%.
- the water-holding capacity is arbitrarily adjustable by way of, for example, selection of pulp fibers, the pretreatment, and the miniaturization treatment.
- the water-holding capacity is measured in accordance with JAPAN TAPPI No. 26: 2000.
- the polylactide to be the graft chain is exemplified by a polymer of L-lactide, a polymer of D-lactide, a random or block copolymer of L-lactide and D-lactide, and the like.
- the polylactide-grafted cellulose nanofiber is insoluble in most solvents, and is not molten even after being heated; therefore, a structural analysis thereof through molecular weight determination by a GPC process or determination on NMR is impossible.
- the absorbency ratio is determined by measuring the IR spectrum after purifying the polylactide-grafted cellulose nanofiber with a solvent such as dichloromethane and tetrahydrofuran that is capable of dissolving the polylactide to completely eliminate the polylactide not being grafted.
- the absorbency ratio being less than 0.01 is not preferred since characteristics as the polylactide are less likely to be exhibited.
- the upper limit of the absorbency ratio may be typically 1,000, and more preferably 300. When the absorbency ratio is greater than 1,000, characteristics of cellulose are tend to be hardly found.
- the polylactide-grafted cellulose nanofiber is suitable as a biodegradable molding material, and as an additive of a molding material. Therefore, the polylactide-grafted cellulose nanofiber can be used: for processing to provide various types of molded products by a procedure such as injection molding, extrusion molding or blow molding; and as an additive of a resinous material such as a polylactide.
- the polylactide-grafted cellulose nanofiber and the molding material to which the fiber is added may be used not only as an injection molded product such as a vessel, but also as a compression molded product, an extrusion molded product, a blow molded product or the like, in the form of a sheet, a film, a foamed material, fibers and the like.
- These molded products may be utilized for intended usage such as electronic parts, building components, civil engineering components, agricultural materials, automobile parts, daily necessities, and the like.
- the polylactide-grafted cellulose nanofiber may be used not only as an organic filler but also as an additive for improving performances of various types of materials, such as a nucleating agent, a crystallization retardation agent, a foamed material improving agent, a film improving agent, and the like.
- the polylactide-grafted cellulose nanofiber may be also used as a biodegradable adhesive.
- the production method of a polylactide-grafted cellulose nanofiber is described.
- graft polymerization of a lactide to cellulose constituting a cellulose nanofiber is carried out in the presence of an organic polymerization catalyst to provide a polylactide-grafted cellulose nanofiber.
- the production method of a polylactide-grafted cellulose nanofiber includes a step of carrying out graft polymerization of a lactide to the aforementioned cellulose having a hydroxyl group, in the presence of an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid.
- a ring-opened lactide is polymerized via an ester bond to each hydroxyl group of the cellulose constituting the cellulose nanofiber in the presence of the organic polymerization catalyst to give the polylactide as a graft chain.
- the organic polymerization catalyst includes an amine and a salt obtained by reacting the amine with an acid
- the graft polymerization reaction of the polylactide to the cellulose proceeds in a living polymerization manner, thereby enabling the polylactide-grafted cellulose nanofiber to be obtained accompanied by molecular weight distribution of the polylactide with a sharp pattern.
- Examples of the amine in the organic polymerization catalyst include: alkylamines such aa methylamine, triethylamine and ethylenediamine; aromatic amines such as aniline; heterocyclic amines such as pyrrolidine, imidazole and pyridine; amine derivatives such as an ether amine and an amino acid; and the like.
- alkylamines such aa methylamine, triethylamine and ethylenediamine
- aromatic amines such as aniline
- heterocyclic amines such as pyrrolidine, imidazole and pyridine
- amine derivatives such as an ether amine and an amino acid
- 4-dimethylaminopyridine is preferred from the viewpoint of enabling the graft polymerization reaction of the polylactide to cellulose constituting a cellulose nanofiber to be more promoted.
- Examples of the acid in the organic polymerization catalyst include: inorganic acids such as hydrochloric acid; sulfonic acids such as p-toluenesulfonic acid and trifluoromethanesulfonic acid; carboxylic acids such as acetic acid; and the like.
- inorganic acids such as hydrochloric acid
- sulfonic acids such as p-toluenesulfonic acid and trifluoromethanesulfonic acid
- carboxylic acids such as acetic acid
- trifluoromethanesulfonic acid is more preferred.
- Examples of the salt obtained by reacting the amine with the acid in the organic polymerization catalyst include 4-dimethylaminopyridinium triflate, 4-dimethylaminopyridinium tosylate, 4-dimethylaminopyridinium chloride, and the like. Of these, in light of a capability of more promoting the graft polymerization reaction for the polylactide to cellulose constituting the cellulose nanofiber, 4-dimethylaminopyridinium triflate is preferred.
- the polylactide-grafted cellulose nanofiber can be synthesized according to the following scheme, for example.
- n and m are each an integer of no less than 1.
- L-lactide, D-lactide or a combination thereof may be used as the lactide.
- the form of the polymer which may be adopted involves: L-polylactide or D-polylactide each obtained when L-lactide or D-lactide is used alone; a random copolymer in which the sequence order of L-lactide and D-lactide is random, which is obtained when L-lactide and D-lactide are used in combination; and a block copolymer in which L-lactide and D-lactide are polymerized block-wise in an arbitrary proportion.
- the graft polymerization step is repeated multiple times in a case in which the grafting percentage is to be increased.
- the graft polymerization reaction for the polylactide to the cellulose nanofiber can efficiently proceed, whereby the mass productivity of the polylactide-grafted cellulose nanofiber is more improved.
- repeating the step necessary times is also possible.
- the polylactide-grafted cellulose nanofiber is obtained by the graft polymerization step, the polylactide not being grafted (ungrafted polylactide) is also included.
- the polylactide-grafted cellulose nanofiber may be used in the state of including the ungrafted polylactide; however, in order to more exert the characteristics of the polylactide-grafted cellulose nanofiber, it is preferred that the production method further includes a purification step for completely eliminating the ungrafted polylactide.
- a solvent for use in the purification step is not particularly limited as long as the polylactide is dissolved, and dichloromethane, tetrahydrofuran or a combination thereof is preferably used.
- the polylactide-grafted cellulose nanofiber that is biodegradable and suitable as both a molding material and a surface-modified organic additive material can be certainly produced.
- the present invention is not limited to the embodiments described above, and may be put into practice in not only the above modes but in modes having been variously altered and/or modified.
- the peak intensity on the IR spectrum was measured under the following conditions.
- a raw material pulp (LBKP, solid content: 2% by mass) was subjected to a pretreatment with a beater for paper making, and thereafter a miniaturization treatment was carried out by using a high-pressure homogenizer to a level of having a single peak in pseudo particle size distribution by a particle size distribution measurement through using laser diffraction (most frequently found diameter: 30 ⁇ m), whereby a dispersion of cellulose nanofiber (hereinafter, referred to as "CNF”) in water having a solid content of 2% by mass was produced.
- CNF dispersion of cellulose nanofiber
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 41 mg.
- the glass transition temperature of the polylactide-grafted CNF of Example 2 was 51.1 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 27 mg.
- the glass transition temperature of the polylactide-grafted CNF of Example 3 was 51.6 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 14 mg.
- the glass transition temperature of the polylactide-grafted CNF of Example 4 was 51.2 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 5 mg.
- Polylactide-grafted CNF was obtained in a similar manner to Example 6 except that 5 mg of the polylactide-grafted CNF of Example 2 was used in place of 5 mg of the polylactide-grafted CNF of Example 1.
- Polylactide-grafted CNF was obtained in a similar manner to Example 6 except that 5 mg of the polylactide-grafted CNF obtained in Example 3 was used in place of 5 mg of the polylactide-grafted CNF obtained in Example 1.
- Example 6 polylactide-grafted CNF of Example 1 5 27 11.2
- Example 7 polylactide-grafted CNF of Example 2 5 11 8.8
- Example 8 polylactide-grafted CNF of Example 3 5 5 6.6
- One function expected for the polylactide-grafted CNF obtained according to the present invention is a retardation or facilitation effect on crystallization of a resin.
- the crystallization temperature and the heat for melting of the commercially available polylactide may be affected, and may in turn be expected to result in an improvement of moldability of the resin mixture.
- the crystallization temperature and the heat for melting were determined to examine the effects on the commercially available polylactide by adding the polylactide-grafted CNF.
- the crystallization temperature and the heat for melting were determined by a DSC method.
- the heat for melting was calculated in terms of an endothermic energy amount (J) per mass (g) of the polylactide component included in the measurement sample. It is to be noted that as the commercially available polylactide, a pulverized polylactide manufactured by Osaka Gas Liquid Co., Ltd. was used.
- Example 3 With 0.1 mg of the polylactide-grafted CNF obtained in Example 3, 4.98 mg of the commercially available polylactide was mixed. From the results of DSC of Example 9, the crystallization temperature was 129 °C, and the heat for melting was 0.15 J/g.
- Example 3 With 0.23 mg of the polylactide-grafted CNF obtained in Example 3, 4.9 mg of the commercially available polylactide was mixed. From the results of DSC of Example 10, the crystallization temperature was 130 °C, and the heat for melting was 0.20 J/g.
- Example 3 With 0.98 mg of the polylactide-grafted CNF obtained in Example 3, 4.93 mg of the commercially available polylactide was mixed. From the results of DSC of Example 11, the crystallization temperature was 129 °C, and the heat for melting was 0.21 J/g.
- Comparative Example 2 was similar to Example 9 except that 0.3 mg of ungrafted CNF was used in place of the polylactide-grafted CNF, and mixed with 13.4 mg of the commercially available polylactide. From the results of DSC of Comparative Example 2, the crystallization temperature was 121 °C, and the heat for melting was 2.26 J/g.
- the polylactide-grafted cellulose nanofiber of the present invention can be suitably used as a biodegradable molding material and a surface-modified organic additive material.
Abstract
Description
- The present invention relates to a polylactide-grafted cellulose nanofiber and a production method thereof.
- In recent years, from the perspective of conservation of global environment, biodegradable polymers that can be decomposed in natural environment due to actions of microorganisms existing in soil and water have attracted attention, and a variety of biodegradable polymers are developed. Atypical example of the biodegradable polymer is a polylactide. The polylactide is characterized by comparatively low cost, and is expected as a biodegradable polymer that is melt moldable. In addition, production of a lactide that is a starting monomer of the polylactide at low cost has been enabled recently by a fermentation process in which a microorganism is used, thereby enabling the polylactide to be produced at an even further low cost, and thus use thereof as not only a biodegradable polymer but also a multipurpose polymer has been investigated.
- On the other hand, although the polylactide has superior characteristics among the biodegradable polymers, due to having properties of being rigid and comparatively fragile as well as poorly flexible, compared with multipurpose polymers, it is necessary to add a softening agent in cases of manufacturing a molded product using the polylactide as a raw material. In addition, the polylactide has still insufficient heat resistance, and somewhat lacks in microwave-oven resistance. Furthermore, the polylactide also has properties of insufficient melting characteristics required in extrusion molding as well as blow molding and expansion molding.
- In this regard, a technique of obtaining a resin composition superior in color tone and mechanical characteristics by melt kneading of a polylactide resin and a naturally-occurring organic filler under a specific condition is disclosed (see Japanese Unexamined Patent Application, Publication No.
2005-35134 - Patent Document 1: Japanese Unexamined Patent Application, Publication No.
2005-35134 - However, such a naturally-occurring organic filler as in the prior art described above is likely to have a hydrophilic surface, and thus tends to be inferior in dispersibility into a molding resin that is highly hydrophobic. Furthermore, in a case in which mechanical strength such as a flexural property is improved, toughness and flexibility may be impaired. Therefore, the molding material should have favorable strength and flexibility and should essentially enable the filler surface to be hydrophobilized in manufacturing a molded product, and thus various surface hydrophobilization treatments have been attempted. Additionally, mere surface hydrophobilization is hardly effective when shearing force is generated between the filler surface and the molding resin. Therefore, for imparting sufficient mechanical properties, strong interaction with an organic material such as a resin is required through, for example, providing the organic filler having a sufficiently long organic molecular chain.
- The present invention was made in view of the foregoing circumstances, and an object of the invention is to provide a polylactide-grafted cellulose nanofiber that is suitable as a molding material, and a production method thereof.
- According to an aspect of the invention made for solving the aforementioned problems, a polylactide-grafted cellulose nanofiber includes grafted cellulose having a graft chain bonding to cellulose constituting a cellulose nanofiber, wherein the graft chain is a polylactide, and a ratio of an absorbance derived from C=O of the polylactide to an absorbance derived from O-H of the cellulose on an infrared absorption spectrum is no less than 0.01 and no greater than 1,000.
- The polylactide-grafted cellulose nanofiber includes grafted cellulose, in which a graft chain bonding to the cellulose is a polylactide. Since the ratio of the absorbance derived from C=O of the carbonyl group included in the polylactide to an absorbance derived from O-H of the hydroxyl group included in cellulose on an infrared absorption spectrum is no less than 0.01 and no greater than 1,000, suitable performances as a molding material can be obtained in addition to biodegradability and rigidity of the polylactide. Moreover, in addition to use as a molding material alone, the polylactide-grafted cellulose nanofiber enables a suitable performance to be attained also as a surface-modified organic additive. The "cellulose nanofiber" as referred to herein means a fine cellulose fiber that can be obtained by defibration of a biomass such as pulp fibers, and in general, means a cellulose fiber that includes cellulose fine fibers having a width of nano size (no less than 1 nm and no greater than 1,000 nm).
- According to other aspect of the present invention made for solving the aforementioned problems, a production method of a polylactide-grafted cellulose nanofiber includes carrying out graft polymerization of a lactide to cellulose constituting a cellulose nanofiber in the presence of an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid.
- In the production method of a polylactide-grafted cellulose nanofiber, an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid is used as a catalyst for the graft polymerization. As a result, a graft polymerization reaction of the polylactide to the cellulose proceeds in a living polymerization manner, thereby enabling the polylactide-grafted cellulose nanofiber to be obtained accompanied by molecular weight distribution of the polylactide with a sharp pattern.
- As the organic polymerization catalyst, 4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate are preferred. When 4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate are used as the organic polymerization catalyst, the graft polymerization reaction of the polylactide to the cellulose described above can be more promoted.
- In the production method of a polylactide-grafted cellulose nanofiber, the graft polymerization is preferably repeated multiple times. Through the graft polymerization repeated multiple times, the production method of a polylactide-grafted cellulose nanofiber enables the graft polymerization reaction of the polylactide to the cellulose nanofiber to proceed efficiently, and therefore mass productivity of the polylactide-grafted cellulose nanofiber is more improved.
- The polylactide-grafted cellulose nanofiber and the production method of the aspects of the present invention enable a polylactide-grafted cellulose nanofiber that is suitable as a molding material and a surface-modified organic additive material to be obtained.
- Hereinafter, the polylactide-grafted cellulose nanofiber and a production method thereof according to embodiments of the present invention are described in detail.
- The polylactide-grafted cellulose nanofiber includes grafted cellulose having a graft chain bonding to cellulose constituting a cellulose nanofiber, in which the graft chain is a polylactide. Moreover, a ratio of the absorbance derived from C=O of the carbonyl group included in the polylactide to an absorbance derived from O-H of the hydroxyl group included in cellulose on an infrared absorption spectrum of the polylactide-grafted cellulose nanofiber is no less than 0.01 and no greater than 1,000.
- The cellulose nanofiber (hereinafter, may be also referred to as "CNF") is a fiber that includes fine fibers obtained by subjecting a biomass such as pulp fibers that include cellulose to a chemical or mechanical treatment. As a production method of the cellulose nanofiber, there exist options in which cellulose per se is modified, and in which cellulose is not modified. In exemplary methods in which cellulose per se is modified, a part of hydroxyl groups of cellulose is modified to a carboxy group, a phosphoric acid ester group, etc. Of these, the method in which cellulose per se is not modified is preferred, and the reason therefor may be inferred as in the following, for example. In a polymerization reaction for a polylactide, a hydroxyl group serves as a starting point, whereas a carboxy group serves as a termination point. Since a cellulose nanofiber is used as an initiator for the polylactide-grafted cellulose nanofiber, a hydroxyl group of the cellulose nanofiber serves as the starting point of the reaction. Therefore, in the case in which a part of the hydroxyl groups of the cellulose is modified to a carboxy group, a phosphoric acid ester group, etc., the starting points of the graft polymerization reaction of the polylactide decrease, and thus the cellulose nanofiber not having been chemically modified is preferably used. The cellulose nanofiber not having been chemically modified is exemplified by a cellulose nanofiber microfabricated by a mechanical treatment. The modification amount of the hydroxyl groups of the cellulose nanofiber obtained is preferably no greater than 0.5 mmol/g, more preferably no greater than 0.3 mmol/g, and still more preferably no greater than 0.1 mmol/g.
- Examples of the pulp fiber include:
- chemical pulp, e.g., hardwood kraft pulp (LKP) such as hardwood bleached kraft pulp (LBKP) and hardwood unbleached kraft pulp (LUKP), needle-leaved kraft pulps (NKP) such as needle-leaved bleached kraft pulp (NBKP) and needle-leaved unbleached kraft pulp (NUKP), and the like;
- mechanical pulps such as stone-ground pulp (SGP), pressurized stone-ground pulp (PGW), refiner-ground pulp (RGP), chemi-ground pulp (CGP), thermo-ground pulp (TGP), ground pulp (GP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP) and bleached thermomechanical pulp (BTMP).
- Of these, bleached chemical pulp (LBKP, NBKP) is preferably used which contains as a principal component, cellulose having a large number of hydroxyl groups that serve as starting points of the reaction of polymerization for the polylactide.
- Prior to microfabrication by a mechanical treatment of the pulp fiber in a slurry, a chemical or mechanical pretreatment may be carried out in an aqueous system. The pretreatment is carried out for reducing the energy for mechanical defibration in the microfabrication step which will follow. The pretreatment is not particularly limited as long as a procedure for the pretreatment is employed in which modification of a functional group of cellulose of the cellulose nanofiber is not caused, and the reaction in an aqueous system enabled. As described above, the cellulose nanofiber is preferably produced by a method in which the functional group of cellulose is not modified. For example, there exists a method in which a primary hydroxyl group of cellulose is preferentially oxidized by using a treatment agent in the chemical pretreatment of the pulp fiber in the slurry, with an N-oxyl compound such as a 2,2,6,6-tetramethyl-1-piperidine-N-oxy (TEMPO) radical as a catalyst, as well as a method in which a phosphoric acid-based chemical is used to modify the hydroxyl group with a phosphoric acid ester group. However, according to these methods, defibration to a level of single nano order (several nm) fiber diameter occurs at once when the mechanical defibration is conducted, and thus carrying out a miniaturization treatment may be difficult to meet a desired fiber size. Furthermore, it is considered that by decreasing the hydroxyl group that serves as the starting point of the reaction as described above, the polymerization reaction of the polylactide may be difficult to proceed. Therefore, a production method is desired in which mechanical defibration is carried out in combination with a mild chemical treatment not leading to modification of the hydroxyl group of cellulose, such as hydrolysis using, for example, a mineral acid (hydrochloric acid, sulfuric acid, phosphoric acid, etc.), an enzyme or the like. By adjusting degrees of the chemical pretreatment and the mechanical defibration, the miniaturization treatment can be carried out to meet a desired fiber size. In addition, by carrying out a pretreatment in an aqueous system, cost for recovery and/or elimination of the solvent can be reduced. The pretreatment may be carried out in concurrence with the chemical pretreatment, or in combination with the mechanical pretreatment (defibration treatment).
- The cellulose nanofibers exhibit a single peak on a pseudo particle size distribution curve obtained by a measurement with a laser diffraction method in a state of having been dispersed in water. The particle diameter corresponding to the peak on the pseudo particle size distribution curve (i.e., most frequently found diameter) is preferably no less than 5 µm and no greater than 60 µm. In the case in which the cellulose nanofibers exhibit such particle size distribution, favorable performances owing to sufficient microfabrication can be achieved. It is to be noted that "pseudo particle size distribution curve" as referred to herein means a curve indicating particle size distribution based on the volume as measured by using a particle size distribution measuring equipment (for example particle size distribution analyzer of laser diffraction scattering type, available from Seishin Enterprise Co., Ltd.).
- It is desired that the average fiber diameter of the cellulose nanofibers is no less than 4 nm and no greater than 1,000 nm. It is considered that through miniaturization of the fibers to the average fiber width described above, the number of fibers in a molten resin per weight is increased, thereby enabling contribution to an increase in melt viscosity of the resin.
- The average fiber diameter is measured by the following method.
- One hundred milliliter of a dispersion liquid of the cellulose nanofibers in water having a solid content concentration of no less than 0.01% by mass and no greater than 0.1% by mass is filtered through a membrane filter made of Teflon (registered trademark), and solvent replacement is conducted with t-butanol. Next, freeze drying is carried out and coating with a metal such as osmium gives a sample for observation. With respect to this sample, an observation is performed by electron microscopic SEM imaging at any magnification of 3,000 times, 5,000 times, 10,000 times or 30,000 times, in accordance with widths of constituting fibers. Specifically, two diagonal lines are drawn on an image for observation, and three straight lines that pass the intersection of the diagonal lines are arbitrarily drawn. Furthermore, widths of 100 fibers in total that cross these three straight lines are measured by visual inspection. Then, a middle diameter of the measurements is determined as the average fiber diameter.
- The lower limit of the degree of crystallization of the cellulose nanofibers is preferably 10%, more preferably 15%, and still more preferably 20%. When the degree of crystallization is less than 10%, the strength of the fibers per se is deteriorated, and therefore an effect of improving the melt viscosity may be impaired.
- On the other hand, the upper limit of the degree of crystallization of the cellulose nanofibers is not particularly limited, but is preferably no greater than 95%, and more preferably no greater than 90%. When the degree of crystallization is greater than 95%, a proportion of strong hydrogen bonds in molecules is increased, whereby the fibers per se can be rigid; however, it is considered that the chemical modification of the cellulose nanofibers may be difficult. It is to be noted that degree of crystallization is arbitrarily adjustable by way of, for example, selection of pulp fibers, the pretreatment, the miniaturization treatment, etc. The degree of crystallization is a value measured by a X-ray diffraction analysis in accordance with "general rules for X-ray diffraction analysis" of JIS-K0131 (1996). It is to be noted that cellulose nanofiber has amorphous parts and crystalline parts, and the degree of crystallization means the proportion of crystalline parts in the entirety of the cellulose nanofibers.
- The lower limit of the pulp viscosity of the cellulose nanofiber is preferably 0.1 cps, and more preferably 0.5 cps. When the pulp viscosity is less than 0.1 cps, resulting from a low degree of polymerization of the cellulose nanofibers, a fibrous state may not be maintained during the polymerization reaction for the polylactide, and the effect of improving the melt viscosity may be impaired.
- In addition, the upper limit of the pulp viscosity of the cellulose nanofiber is preferably 50 cps, and more preferably 40 cps. When the pulp viscosity is greater than 50 cps, the degree of polymerization of the cellulose nanofiber per se is so great that the fiber is too long, whereby sufficient inhibition of aggregation of cellulose nanofibers may fail in the polymerization reaction for the polylactide, and thus the polymerization reaction for the polylactide may proceed nonuniformly. The pulp viscosity is measured in accordance with JIS-P8215 (1998). It is to be noted that a greater pulp viscosity indicates a greater degree of polymerization of the cellulose.
- In the case in which a solid content concentration of the cellulose nanofibers in the solution is 1% by mass, the lower limit of type B viscosity of the dispersion liquid is preferably 1 cps, more preferably 3 cps, and still more preferably 5 cps. When the type B viscosity of the dispersion liquid is less than 1 cps, the fibrous state may not be maintained during the polymerization reaction for the polylactide, and the effect of improving the melt viscosity may be impaired.
- Meanwhile, the upper limit of the type B viscosity of the dispersion liquid is preferably 7,000 cps, more preferably 6,000 cps, and still more preferably 5,000 cps. When the type B viscosity of the dispersion liquid is greater than 7,000 cps, enormous energy is required for pumping up for transfer of a dispersion in water, whereby the production cost may be increased. The type B viscosity is measured on a dispersion liquid of the cellulose nanofibers in water having a solid content concentration of 1%, in accordance with "methods for viscosity measurement of liquid" of JIS-Z8803 (2011). The type B viscosity is a resistance torque in stirring a slurry, and a greater type B viscosity indicates a greater energy being required for the stirring.
- The upper limit of the water-holding capacity of the cellulose nanofiber is preferably 600%, more preferably 580%, and still more preferably 560%. When the water-holding capacity is greater than 600%, efficiencies of solvent replacement and drying are deteriorated, which may lead to an increase in production cost. The water-holding capacity is arbitrarily adjustable by way of, for example, selection of pulp fibers, the pretreatment, and the miniaturization treatment. The water-holding capacity is measured in accordance with JAPAN TAPPI No. 26: 2000.
- The polylactide to be the graft chain is exemplified by a polymer of L-lactide, a polymer of D-lactide, a random or block copolymer of L-lactide and D-lactide, and the like.
- The polylactide-grafted cellulose nanofiber is insoluble in most solvents, and is not molten even after being heated; therefore, a structural analysis thereof through molecular weight determination by a GPC process or determination on NMR is impossible. Thus, by way of the measurement of an infrared ray absorption (hereinafter, may be also referred to as IR) spectrum, a ratio of an absorbance derived from C=O of the polylactide to an absorbance derived from O-H of the cellulose (hereinafter, may be also merely referred to as "absorbency ratio") of the polylactide-grafted cellulose nanofiber is determined, and used as a marker of the degree of grafting. The absorbency ratio is determined by measuring the IR spectrum after purifying the polylactide-grafted cellulose nanofiber with a solvent such as dichloromethane and tetrahydrofuran that is capable of dissolving the polylactide to completely eliminate the polylactide not being grafted. The lower limit of the ratio of the absorbance derived from C=O of the polylactide to the absorbance derived from O-H of the cellulose on the IR spectrum of the polylactide-grafted cellulose nanofiber is typically 0.01, and more preferably 0.05. The absorbency ratio being less than 0.01 is not preferred since characteristics as the polylactide are less likely to be exhibited. The upper limit of the absorbency ratio may be typically 1,000, and more preferably 300. When the absorbency ratio is greater than 1,000, characteristics of cellulose are tend to be hardly found.
- The polylactide-grafted cellulose nanofiber is suitable as a biodegradable molding material, and as an additive of a molding material. Therefore, the polylactide-grafted cellulose nanofiber can be used: for processing to provide various types of molded products by a procedure such as injection molding, extrusion molding or blow molding; and as an additive of a resinous material such as a polylactide.
- In addition, with respect to the intended usage, the polylactide-grafted cellulose nanofiber and the molding material to which the fiber is added may be used not only as an injection molded product such as a vessel, but also as a compression molded product, an extrusion molded product, a blow molded product or the like, in the form of a sheet, a film, a foamed material, fibers and the like. These molded products may be utilized for intended usage such as electronic parts, building components, civil engineering components, agricultural materials, automobile parts, daily necessities, and the like. In addition, the polylactide-grafted cellulose nanofiber may be used not only as an organic filler but also as an additive for improving performances of various types of materials, such as a nucleating agent, a crystallization retardation agent, a foamed material improving agent, a film improving agent, and the like. Furthermore, the polylactide-grafted cellulose nanofiber may be also used as a biodegradable adhesive.
- Next, the production method of a polylactide-grafted cellulose nanofiber is described. According to the production method of a polylactide-grafted cellulose nanofiber, graft polymerization of a lactide to cellulose constituting a cellulose nanofiber is carried out in the presence of an organic polymerization catalyst to provide a polylactide-grafted cellulose nanofiber. More specifically, the production method of a polylactide-grafted cellulose nanofiber includes a step of carrying out graft polymerization of a lactide to the aforementioned cellulose having a hydroxyl group, in the presence of an organic polymerization catalyst which includes an amine and a salt obtained by reacting the amine with an acid. In the graft polymerization step, a ring-opened lactide is polymerized via an ester bond to each hydroxyl group of the cellulose constituting the cellulose nanofiber in the presence of the organic polymerization catalyst to give the polylactide as a graft chain.
- According to the production method of a polylactide-grafted cellulose nanofiber, since the organic polymerization catalyst includes an amine and a salt obtained by reacting the amine with an acid, the graft polymerization reaction of the polylactide to the cellulose proceeds in a living polymerization manner, thereby enabling the polylactide-grafted cellulose nanofiber to be obtained accompanied by molecular weight distribution of the polylactide with a sharp pattern.
- Examples of the amine in the organic polymerization catalyst include: alkylamines such aa methylamine, triethylamine and ethylenediamine; aromatic amines such as aniline; heterocyclic amines such as pyrrolidine, imidazole and pyridine; amine derivatives such as an ether amine and an amino acid; and the like. Of these, 4-dimethylaminopyridine is preferred from the viewpoint of enabling the graft polymerization reaction of the polylactide to cellulose constituting a cellulose nanofiber to be more promoted.
- Examples of the acid in the organic polymerization catalyst include: inorganic acids such as hydrochloric acid; sulfonic acids such as p-toluenesulfonic acid and trifluoromethanesulfonic acid; carboxylic acids such as acetic acid; and the like. With respect to the acid, since higher acidity leads to a greater catalytic activity, p-toluenesulfonic acid and trifluoromethanesulfonic acid are preferred among the acids exemplified above, and of these, trifluoromethanesulfonic acid is more preferred.
- Examples of the salt obtained by reacting the amine with the acid in the organic polymerization catalyst include 4-dimethylaminopyridinium triflate, 4-dimethylaminopyridinium tosylate, 4-dimethylaminopyridinium chloride, and the like. Of these, in light of a capability of more promoting the graft polymerization reaction for the polylactide to cellulose constituting the cellulose nanofiber, 4-dimethylaminopyridinium triflate is preferred.
- By using 4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate as the organic polymerization catalyst in the production method of a polylactide-grafted cellulose nanofiber, the effect of more promoting the graft polymerization reaction for the polylactide to the cellulose nanofiber can be further enhanced.
-
- In the above scheme, n and m are each an integer of no less than 1. As described above, L-lactide, D-lactide or a combination thereof may be used as the lactide. The form of the polymer which may be adopted involves: L-polylactide or D-polylactide each obtained when L-lactide or D-lactide is used alone; a random copolymer in which the sequence order of L-lactide and D-lactide is random, which is obtained when L-lactide and D-lactide are used in combination; and a block copolymer in which L-lactide and D-lactide are polymerized block-wise in an arbitrary proportion.
- In the production method of a polylactide-grafted cellulose nanofiber, it is preferred that the graft polymerization step is repeated multiple times in a case in which the grafting percentage is to be increased. By repeating the graft polymerization step multiple times, the graft polymerization reaction for the polylactide to the cellulose nanofiber can efficiently proceed, whereby the mass productivity of the polylactide-grafted cellulose nanofiber is more improved. For example, by repeating the graft polymerization step twice, the polylactide-grafted cellulose nanofiber can be efficiently produced, with the ratio of an absorbance derived from C=O of the polylactide to an absorbance derived from O-H of the cellulose on the IR spectrum of the polylactide-grafted cellulose nanofiber being no less than 0.01 and no greater than 1,000. When a further increase in the grafting percentage is intended, repeating the step necessary times is also possible.
- After the polylactide-grafted cellulose nanofiber is obtained by the graft polymerization step, the polylactide not being grafted (ungrafted polylactide) is also included. The polylactide-grafted cellulose nanofiber may be used in the state of including the ungrafted polylactide; however, in order to more exert the characteristics of the polylactide-grafted cellulose nanofiber, it is preferred that the production method further includes a purification step for completely eliminating the ungrafted polylactide. A solvent for use in the purification step is not particularly limited as long as the polylactide is dissolved, and dichloromethane, tetrahydrofuran or a combination thereof is preferably used.
- According to the production method of a polylactide-grafted cellulose nanofiber, the polylactide-grafted cellulose nanofiber that is biodegradable and suitable as both a molding material and a surface-modified organic additive material can be certainly produced.
- The present invention is not limited to the embodiments described above, and may be put into practice in not only the above modes but in modes having been variously altered and/or modified.
- Hereinafter, the present invention is more specifically described by way of Examples, but the present invention is not limited to the following Examples.
- The ratio of an absorbance derived from C=O of the polylactide to an absorbance derived from O-H of the cellulose on an IR spectrum was determined. The peak intensity on the IR spectrum was measured under the following conditions.
- IR measurement conditions
- apparatus: Fourier transform infrared spectrometer FT-IR6700 manufactured by Nicolet and DURASCOPE
- manufactured by SensIR Technologies
- optical resolution: 4 cm-1
- integration count: 32
- measuring method: ATR method
- measurement absorbance: O-H deriving peak: around 3,680 cm-1 to 3,000 cm-1 C=O deriving peak: around 1,890 cm-1 to 1,520 cm-1
- Measurement of the glass transition temperature, the crystallization temperature, and the heat for melting was performed by a DSC method under the conditions below. It is to be noted that the data presented in Table 3 below show results obtained in course (3) in the following temperature program (for one measurement, temperature up and temperature down were executed in the order of (1), (2), (3) below).
- apparatus: EXSTAR DSC6200, manufactured by Hitachi High-Technologies Corporation
- nitrogen flow rate: 40 ml/min.
- temperature up and cooling conditions: temperature up and temperature down being executed continuously in the order of (1), (2), (3).
rate of temperature up and temperature down: 10 °C/min.- (1) 10 °C to 200 °C
- (2) 200 °C to 10 °C
- (3) 10 °C to 200 °C
- standard substance: alumina powder
- sample container: open aluminum pan
- sample mass: about 5 mg
- In a two-neck flask (volume: 100 ml), 1.22 g of 4-dimethylaminopyridine (manufactured by Tokyo Chemical Industry Co., Ltd., white powder) was dissolved in 20 ml of tetrahydrofuran in a dry nitrogen atmosphere. Subsequently, 1.50 g of trifluoromethanesulfonic acid was added dropwise and the mixture was stirred while the two-neck flask was cooled in a ice-cooling bath at 0 °C. Thereafter, the temperature was allowed to be the room temperature, and the stirring was continued for 1 hour. The reaction mixture was filtered through a glass filter, washed with 10 ml of tetrahydrofuran twice, and then dried under reduced pressure to give quantitatively 4-dimethylaminopyridinium triflate as white powder.
- A raw material pulp (LBKP, solid content: 2% by mass) was subjected to a pretreatment with a beater for paper making, and thereafter a miniaturization treatment was carried out by using a high-pressure homogenizer to a level of having a single peak in pseudo particle size distribution by a particle size distribution measurement through using laser diffraction (most frequently found diameter: 30 µm), whereby a dispersion of cellulose nanofiber (hereinafter, referred to as "CNF") in water having a solid content of 2% by mass was produced. After the CNF dispersion in water was subjected to a centrifugal separator, the supernatant liquid was eliminated, a solvent was added thereto, followed by homogenization and centrifugal separation again to permit concentration. This operation was repeated several times followed by freeze drying to remove the solvent. Accordingly, CNF was prepared as white powder.
- Into a two-neck flask (volume: 50 ml), 54 mg of CNF white powder, 6.1 mg (0.05 mmol) of 4-dimethylaminopyridine (manufactured by Tokyo Chemical Industry Co., Ltd.) white powder, 13.6 mg (0.05 mmol) of 4-dimethylaminopyridinium triflate synthesized as described above, and 720 mg (5 mmol) of colorless and transparent rod-shape crystalline L-lactide were added in a dry-nitrogen atmosphere. The two-neck flask was then heated in an oil bath at 100 °C for 1 hour to give a colorless and transparent solid.
- The colorless and transparent solid thus obtained was dissolved in 10 ml of dichloromethane, and the insoluble matter was recovered by filtration on a glass filter. To the filter residue, 20 mL of tetrahydrofuran was added, and subjected to a centrifugal separator (H-200, manufactured by KOKUSAN Co. Ltd., at 5,000 rpm for 15 min). Thereafter, the supernatant was removed, and 20 mL of tetrahydrofuran was added again and the mixture was subjected to the centrifugal separator by a similar operation followed by removing of the supernatant. Thus, ungrafted polylactide was eliminated to give 52 mg of polylactide-grafted CNF. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 0.8.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 41 mg. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 2.8. The glass transition temperature of the polylactide-grafted CNF of Example 2 was 51.1 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 27 mg. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 5.8. The glass transition temperature of the polylactide-grafted CNF of Example 3 was 51.6 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 14 mg. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 7.1. The glass transition temperature of the polylactide-grafted CNF of Example 4 was 51.2 °C.
- Polylactide-grafted CNF was obtained in a similar manner to Example 1 except that the amount of CNF used was changed to 5 mg. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 3.3.
- Table 1 shows ratios of the absorbance derived from C=O to the absorbance derived from O-H on IR spectra of Examples 1 to 5, and glass transition temperatures. Additionally, the glass transition temperature of CNF alone is shown together in Table 1 as Reference Example 1.
Table 1 CNF Polylactide-grafted CNF Ratio of absorbance derived from C=O to absorbance derived from O-H on IR spectrum Glass transition temperature (°C) used (mg) obtained (mg) Example 1 54 52 0.8 - Example 2 41 39 2.8 51.1 Example 3 27 27 5.8 51.6 Example 4 14 11 7.1 51.2 Example 5 5 5 3.3 - Reference Example 1 (CNF alone) - - - not detected - Into a two-neck flask (volume: 50 ml), 5 mg of the polylactide-grafted CNF of Example 1, 6.1 mg (0.05 mmol) of white powder of 4-dimethylaminopyridine (manufactured by Tokyo Chemical Industry Co., Ltd.), 13.6 mg (0.05 mmol) of 4-dimethylaminopyridinium triflate, and 720 mg (5 mmol) of colorless and transparent rod-shaped crystals of lactide were added in a dry-nitrogen atmosphere. The two-neck flask was then heated in an oil bath at 100 °C for 1 hour to give a colorless and transparent solid.
- The colorless and transparent solid thus obtained was dissolved in 10 ml of dichloromethane, and the insoluble matter was recovered by filtration on a glass filter. To the filter residue, 20 mL of tetrahydrofuran was added, and subjected to a centrifugal separator (H-200, manufactured by KOKUSAN Co. Ltd., at 5,000 rpm for 15 min). Thereafter, the supernatant was removed, and 20 mL of tetrahydrofuran was added again and the mixture was subjected to the centrifugal separator by a similar operation followed by removing of the supernatant. Thus, ungrafted polylactide was completely eliminated to give intended polylactide-grafted CNF (27 mg). The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 11.2.
- Polylactide-grafted CNF was obtained in a similar manner to Example 6 except that 5 mg of the polylactide-grafted CNF of Example 2 was used in place of 5 mg of the polylactide-grafted CNF of Example 1. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 8.8.
- Polylactide-grafted CNF was obtained in a similar manner to Example 6 except that 5 mg of the polylactide-grafted CNF obtained in Example 3 was used in place of 5 mg of the polylactide-grafted CNF obtained in Example 1. The ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum in the polylactide-grafted CNF thus obtained was 6.6.
- Table 2 shows the ratio of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectrum after the grafting of the second step to the polylactide-grafted CNF.
Table 2 Mass of polylactide-grafted Mass of polylactide-grafted Ratio of absorbance derived from C=O to absorbance derived from O-H on IR spectrum CNF used (mg) CNF obtained by second step of grafting (mg) Example 6 polylactide-grafted CNF of Example 1 5 27 11.2 Example 7 polylactide-grafted CNF of Example 2 5 11 8.8 Example 8 polylactide-grafted CNF of Example 3 5 5 6.6 - One function expected for the polylactide-grafted CNF obtained according to the present invention is a retardation or facilitation effect on crystallization of a resin. As one example, when the polylactide-grafted CNF is added as an additive to a commercially available polylactide, the crystallization temperature and the heat for melting of the commercially available polylactide may be affected, and may in turn be expected to result in an improvement of moldability of the resin mixture. Thus, with respect to Examples 9 to 11 below in which the polylactide-grafted CNF was mixed with a commercially available polylactide, the crystallization temperature and the heat for melting were determined to examine the effects on the commercially available polylactide by adding the polylactide-grafted CNF. The crystallization temperature and the heat for melting were determined by a DSC method. The heat for melting was calculated in terms of an endothermic energy amount (J) per mass (g) of the polylactide component included in the measurement sample. It is to be noted that as the commercially available polylactide, a pulverized polylactide manufactured by Osaka Gas Liquid Co., Ltd. was used.
- With 0.1 mg of the polylactide-grafted CNF obtained in Example 3, 4.98 mg of the commercially available polylactide was mixed. From the results of DSC of Example 9, the crystallization temperature was 129 °C, and the heat for melting was 0.15 J/g.
- With 0.23 mg of the polylactide-grafted CNF obtained in Example 3, 4.9 mg of the commercially available polylactide was mixed. From the results of DSC of Example 10, the crystallization temperature was 130 °C, and the heat for melting was 0.20 J/g.
- With 0.98 mg of the polylactide-grafted CNF obtained in Example 3, 4.93 mg of the commercially available polylactide was mixed. From the results of DSC of Example 11, the crystallization temperature was 129 °C, and the heat for melting was 0.21 J/g.
- The commercially available polylactide alone was employed as Comparative Example 1. From the results of DSC of Comparative Example 1, the crystallization temperature was 122 °C, and the heat for melting was 0.97 J/g.
- Comparative Example 2 was similar to Example 9 except that 0.3 mg of ungrafted CNF was used in place of the polylactide-grafted CNF, and mixed with 13.4 mg of the commercially available polylactide. From the results of DSC of Comparative Example 2, the crystallization temperature was 121 °C, and the heat for melting was 2.26 J/g.
Table 3 Mixing ratio of polylactide-grafted CNF and commercially available polylactide Percentage content of CNF in total solid content (% by mass) Crystallization temperature (°C) Heat for melting (J/g) polylactide-grafted CNF of Example 3 ungrafted CNF commercially available polylactide (mg) (mg) (mg) Example 9 0.1 - 4.98 1.0 129 0.15 Example 10 0.23 4.9 2.3 130 0.20 Example 11 0.98 4.93 8.6 129 0.21 Comparative Example 1 4.24 0 122 0.97 Comparative Example 2 0.3 13.4 2.2 121 2.26 - As indicated by the ratios of the absorbance derived from C=O to the absorbance derived from O-H on the IR spectra of Examples 1 to 5 shown in Table 1 above, it was suggested that carrying out the graft polymerization of the polylactide to the cellulose nanofiber at various grafting percentages was enabled. Moreover, as indicated by Examples 6 to 8 shown in Table 2, the ratio of the absorbance derived from C=O to the absorbance derived from O-H was prominently increased by repeating the graft polymerization step twice, revealing that efficient and significant improvement of the grafting percentage of the polylactide was enabled.
- In addition, it was indicated that the mixtures of the polylactide-grafted CNFs of Examples 9 to 11 with the commercially available polylactide had higher crystallization temperatures, and required lower heat for melting than Comparative Example 1 involving the commercially available polylactide alone, and Comparative Example 2 involving the mixture of the ungrafted CNF with the commercially available polylactide.
- The polylactide-grafted cellulose nanofiber of the present invention can be suitably used as a biodegradable molding material and a surface-modified organic additive material.
Claims (4)
- A polylactide-grafted cellulose nanofiber comprising grafted cellulose which comprises a graft chain bonding to cellulose constituting a cellulose nanofiber, wherein
the graft chain is a polylactide, and
a ratio of an absorbance derived from C=O of the polylactide to an absorbance derived from O-H of the cellulose on an infrared absorption spectrum is no less than 0.01 and no greater than 1,000. - A production method of a polylactide-grafted cellulose nanofiber comprising carrying out graft polymerization of a lactide to cellulose constituting a cellulose nanofiber in the presence of an organic polymerization catalyst which comprises an amine and a salt obtained by reacting the amine with an acid.
- The production method of a polylactide-grafted cellulose nanofiber according to claim 2, wherein the organic polymerization catalyst is 4-dimethylaminopyridine and 4-dimethylaminopyridinium triflate.
- The production method of a polylactide-grafted cellulose nanofiber according to claim 2 or 3, wherein the graft polymerization is repeated multiple times.
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